JK Rowling's sixth Harry Potter book will have the highest initial print run in US history, it was announced today.

Harry Potter and the Half-Blood Prince will break its own record when 10.8 million copies hit US bookshelves on July 16.

That's four million more than its record-breaking initial print run for the fifth book in the series, Harry Potter and the Order of the Phoenix, published in 2003.

The book, printed after a three year gap, made publishing history when it sold 5 million copies in 24 hours.

Copies

US publisher, Scholastic, said judging by past experience Potter fans would want the latest instalment of wizardry the moment it goes on sale.

"We wanted to be ready so that every single child, every single person who started out with Harry Potter when it began and every family that wants multiple copies will be able to get them," said Barbara Marcus, president of Scholastic Children's Books.

Speculation about the content of the book is rife, but the new adventures have been kept a closely guarded secret.

Scholastic has revealed only that the Half-Blood Prince will be 672 pages and that the cover of the US edition will feature Harry and Professor Dumbledore.

A multi-million dollar marketing campaign kicks off on April 7 marking the "100 Day Countdown to Harry."